Ion generator using radioactive material



March 12, 1957 T. L. MARTIN, JR 2,785,312

ION GENERATOR USING RADIOACTIVE MATERIAL Filed Sept. 21, 1955 4 d I1 4 55 Pg 2 L Sea/re of [1C 7 t 10 1/ J3 f 15 g 24 i 1 Q gas IN VEN TOR.

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ION GENERATOR USING RADIOACTIVE MATERIAL Thomas L. Martin, 322, Tucson,Ariz., assignor to Ionaire, Inc, San Francisco, (Ialitl, a corporationof California Application September 21, 1953, Serial No. 381,458

8 Claims. (Cl. 250-44) This invention relates to a device for generatingions in air, useful for producing a predominance of light ions of eithersign in the circumambient space.

Generators for this specific purpose are described in a priorapplication filed on June 3, 1953. under Serial No. 359,377, in the nameof Thomas L. Martin, Jr. In that application, the generator utilizes apolonium element or cell, that emits alpha particles, causing bycollision with air molecules light ions of opposite signs. Those ionsundesired sign are absorbed, and the desired ions are blown out by afan. By appropriate choice of potentials on the various electrodesutilized in the device, it is possible to suppress all or nearly all ofthe undesired ions.

For general beneficial effects upon humans, the desired ions are ofnegative sign; but the apparatus may be used to produce predominantlyions of either sign.

Polonium as the active element has many advantages. its radiation isconfined almost entirely to alpha partticles, which do not have greatpenetration power, and accordingly it is easy to guard against harmfulradiations reaching the space w ere the apparatus is located. However,the half-life of polonium is quite limited, and it is accordinglyadvisable to renew the polonium element in less than one year.

It is one of the objects of this invention to provide an ion generatorin which the .active element need be renewed only about every twentyyears, and yet without danger of harmful radiations reaching theatmosphere.

in order to accomplish this result, radioactive material such as radiumD is used as the active emitter. Such material, in addition to emissionof the relatively easily controlled alpha particles, also emits gammaand beta rays. I The radioactive material slowly degenerates topolonium; but at the same time, care must be taken to confine theinjurious gamma and beta radiations to a space where they cannot emergeinto the atmosphere.

it is accordingly another object of this invention to provide astructure that is safe when material such as radium D is used as theactive element.

This invention possesses many other advantages, and has other objectswhich may be made more clearly apparent from a consideration of oneembodiment of the invention. For this purpose, there is shown a form inthe drawings accompanying and forming part of the present specification.The form will now be described in detail, illustrating the generalprinciples of the inventlon; but it is to be understood that thisdetailed description is not to be taken in a limiting sense, since thescope of this invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a longitudinal sectional view of a device incorporating theinvention, and shown connected with a source of potential dillerence;and

Fig. 2 is a cross sectional view, taken along aplane corresponding toline 2-2 of Fig. l.

The ion generator in this instance includes a tubular hired StatesPatent metallic shell 1 serving as an anode. This tubular metallic shellmay be formed of round aluminum tubing. The cathode structure is made ofrod-like metal element 2 supported by the aid of a spider made ofinsulation material, such as Bakelite. The spider is attached to theinside of the electrode 1, near its upper edge.

The spider structure includes a hub member 3, within which electrode 2is firmly supported. A plurality of machine screws 4 are threadedradially into the hub 3, and extend through appropriate apertures inanode 1. Insulation bushings 5 surround the screws 4, and maintain theelectrodes 1 and 2 out of electrical contact. Preferably, threeequiangularly spaced screws 4 may be used.

In order to provide a potential difference between the electrodes 1 and2 use is made of any appropriate source of direct current 7.

When it is desired to operate the device for the generation of negativeions and the suppression of positive ions, the electrode 1 is made theanode and the electrode 2 is made the cathode. Accordingly, ashereinafter explained, when there is a flow of ions upwardly into theinterior of the electrode 1, the positive ions are attracted to thecentral electrode 2. The negative'ions, however, are blown out throughthe top of the tubular electrode 1 by the aid of an appropriatecentrifugal blowerstructure 8.

In order to ionize the atmosphere, use is made of a radioactivematerial. 'In the present instance, this material is in the form of aribbon-like foil 9 incorporating radium D or other equivalent material.The thickness of this foil is greatly exaggerated in the drawing. Thisfoil lines the inner surface of a cylindrical metallic tube 10, such asaluminum, covered with lead of suitable thickness. This tube 10 isprovided with an upper cover member 11 and a lower cover member 12,having central aligned apertures 13 and 14 respectively. These covermembers 11 and 12 may also be made of aluminum or other material,covered with lead of suitable thickness.

The fan 8 has an outlet conduit 15 attached as by flange 19 to theflange 21 of a conical fan adapter 20. This fan adapter may be made ofplastic material, and it has a cylindrical projection 22 attached to theouter surface of anode 1. The fan 8 thus produces a flow of airlongitudinally along the inner surface of this anode. This fiow ofunionized air prevents losses of negative ions that would otherwise beseparated from the stream of ionized air. Of course, there is also aflow of air through the structure 10-1l-12. Fan 8 is intended to producean air movement at the rate of about 400 to 508 feet per minute.

The radioactive foil 9 serves as a source of radiations of alpha, betaand gamma particles. When the foil 9 is arranged as a circular bandhaving a diameter of about six centimeters, the focusing effect is suchthat the area of intense ionization of the air occurs in a circle ofapproximately two centimeters in diameter. Accordingly, the apertures 13and 14 are made of about this size, and axial of the foil 9.

The radioactive material embodied in foil 9 has an extended half-life,so that only at long intervals is it necessary to replace it. Thematerial deteriorates slowly into polonium, which provides a copiousflow of alpha particles.

The alpha, beta, and gamma rays emitted from the radioactive foil 9 areso confined that there is little likelhood of any of these rays escapingthrough the apertures 13 and 14. This efi'ect is enhanced by therelatively short axial length of the band 9. For example, it may beabout one-half centimeter, or approximately one-fourth of an inch.Accordingly, the inner diameter of tube 10 is about ten times the widthor axial length of foil 9. The mean range of the alpha particlesradiated from the foil 9 is sutficiently short so that there is nodanger that these alpha particles can ever extend into the aluminumelectrode 1. In order to ensure that the more powerful beta and gammaradiations be properly confined, appropriate lead sheathing may beprovided, although in most instances such shielding is unnecessary.

In the present instance the tubular structure comprising the tube 10 andcover members 11 and 12 are overlaid with relatively heavy lead covers.Thus there are lead discs 16 and 17 overlying the members 11 and 12.Also, there is a lead annular ring 18 around the periphery of thealuminum member 10. The lead members 16, 17 and 18 are soldered togetherto form an integral shield. The excess solder at the joints is removedto provide a smooth exterior. The lead shield is thus utilizable as acollimator, performing the same functions as the collimator described inthe said prior application. Accordingly, it is connected to source 7 forplacing an appropriate potential upon it. For holding the radioactiveunit in place, use is made of a plurality of nuts 23 soldered to theexterior of ring 18, and equiangularly spaced (Fig. 2). Engaging thesenuts are the screws 24, passing through the anode l, and insulatedtherefrom by insulation sleeves 25.

The shielding structure that supports the radioactive foil is shown asformed of an inner layer of aluminum and an outer layer of lead. This isof value in controlling or reducing the scattering of beta rays emittedfrom the foil. Such rays scatter very little from low density materialssuch as aluminum; but they do scatter from dense material such as lead.Accordingly, incident beta rays will pass through'the aluminum and theywill, to a large extent, be absorbed in the lead.

The characteristics of the device are similar to those described in saidprior application. By appropriate choice of relative potentials of thethree electrodes 1, 2, and 10, the device emits a copious flow of ionsof either desired sign. When only negative ions are desired, the anode 1is made positive with respect to cathode 2; and the potential of thecollimator structures 1@161718 is made still more negative. Thus, asbefore, the potential of cathode 2 may be about 200 volts below that ofanode 1; and the potential of the collimator 10-161718 may be about 425volts below that of anode 1. With such values, the positive ions aresubstantially entirely suppressed.

The inventor claims:

1. In a device for supplying ions of a desired polarity in air: atubular radioactive member; means forming an emission aperture at oneend of the member, said aperture having an area substantially less thanthat bounded by the inner surface of the member; an electrode beyond theaperture and substantially coaxial therewith; means for creating anelectrostatic field between the member and the electrode, such as toattract only those of the resulting ions that have the undesiredpolarity to said electrode; and means for producing a movement of airpast said electrode.

2. In a device for supplying ions of a desired polarity in air: atubular radioactive member; means forming an emission aperture at oneend of the member, said aperture having an area substantially less thanthat bounded by the inner surface of the member; a rod electrode beyondthe aperture and aligned therewith; a tubular-electrode surrounding saidrod electrode; but out of electrical contact with the member and the rodelectrode; means for creating an electrostatic field between the memberand the rod electrode to cause attraction of ions of undesired polarity,to the rod electrode; means for impressing a potential on theradioactiv'e member with respect to the tubular electrode, to repel theions of desired polarity; and means for producing a movement of aidthrough said tubular elec trode. a

3. In a device for supplying ions of a desired polarity in air: atubular radioactive member; means forming an emission aperture at oneend of the member, said aperture having an area substantially less thanthat bounded by the inner surface of the member; a rod electrode beyondthe aperture and substantially coaxial therewith; a tubular electrodesurrounding said rod electrode; a conducting shield for the radioactivemember and in electrical contact therewith; means for impressing apotential on the rod electrode of such polarity as to attract only thoseof the resulting ions that have the undesired polarity; means forimpressing upon the shield a potential to repel the ions of desiredpolarity; means for impressing upon the tubular electrode a potentialrelatively opposite that of the rod electrode; and means for producing amovement of air through the second tubular member.

4. In a device for supplying ions of a desired polarity in air: atubular member; radioactive material within the tubular member andadjacent the inner wall of the memer; a cover for the member having anemission aperture; a rod electrode beyond the aperture and alignedtherewith; a tubular electrode surrounding said rod electrode and thetubular member, and spaced from said tubular member; and means creatinga flow of air adjacent the inner surface of the tubular electrode.

5. In a device for supplying ions of a desired polarity in air: atubular metallic support; a ribbon-like radioactive element supported onthe inner wall of said support; the diameter of the support being of theorder of ten times the width of the element; metal plates overlying theends of the support; the plates having aligned apertures; a rodelectrode extending beyond one of the plates and aligned with theapertures; a cylindrical electrode surrounding the rod electrode and thesupport and out of contact therewith; means for impressing a potentialon the rod electrode of such polarity as to attract only those of theresulting ions that have the undesired polarity; means for impressingupon the support a potential to repel the ions of the desired polarity;means for impressing upon the cylindrical electrode a potentialrelatively opposite that of the rod electrode; and means for producing amovement of air through the cylindrical electrode.

6. In a device for supplying ions of a desired polarity in air: atubular metallic support; a ribbon-like radioactive element supported onthe inner wall of said support; the diameter of the support being of theorder of ten times the width of the element; metal plates overlying theends of the support; the plates having aligned apertures; a rodelectrode extending beyond one of the plates and aligned with theapertures; a cylindrical electrode surrounding the rod electrode; meansfor impressing a potential on the rod electrode of such polarity as toattract only those of the resulting ions that have the undesiredpolarity; means-for impressing upon the support a potential to repel theions of the desired polarity; means for impressing upon the cylindricalelectrode a potential relatively opposite that of the rod electrode; anda fan for within the hollow member and adjacent the inner wall thereof;a covering wall for the member and having an emission aperture; a hollowfirst electrode surrounding said tubular member to form an air passagebetween them; a second electrode within the first electrode and alignedwith said aperture; means for impressing a potential on the secondelectrode of such polarity as to attract only those of the resultingions that have the undesired polarity; means for impressing upon thehollow member a potential to repel the ions of desired polarity; meansfor impressing upon-the first electrode a potential relatively oppositethat of the secondelectrode; and meansv for producing a movement-of airthrough the first electrode.

3. In a device for supplying ions of a desired polarity in air: a hollowmetallic member; radioactive material within the hollow member andadjacent the inner Wall thereof; a covering Wall for the member andhaving an emission aperture; said aperture having an opening with anarea of about one-tenth the area bounded by said inner Wall; a hollowfirst electrode surrounding said tubular member to form an air passagebetween them; a second electrode Within the first electrode and alignedWith said aperture; means for impressing a potential on the secondelectrode of such polarity as to attract only those of the resultingions that have the undesired polarity; means for impressing upon thehollow member a potential to repel the ions of desired polarity; meansfor im- References Cited in the file of this patent UNITED STATESPATENTS 2,381,455 Jacob Aug. 7, 1945 2,594,777 Hicks Apr. 29, 19522,739,283 Roehrig Mar. 20, 1956 OTHER REFERENCES Serial No. 376,930,Peycelon et al. (A. P. (3.), published May 25, 1943.

